Changes in this CL:
 - The version of the control channel is increased to 3. This allows the host and client to tell if the peer supports capabilities negotiation or not.
 - The client and host negotiate supported capabilities by sending each other a list of the supported capabilities. Capabilities supported by both client and host are assumed to be enabled.
 - The client plugin and webapp negotiate the list of capabilities supported by the client. The webapp has the final word.
 - The DesktopEnvironment interface was extended to provide the list of all supported capabilities and receive the results of negotiation with the client.
 - Added the 'sendInitialResolution' capability. When it is enabled the client sends its screen resolution to the host once the connection has been established.
 - DesktopSessionProxy now waits for the client screen resolution when the 'sendInitialResolution' capability is enabled.

BUG=230893

Review URL: https://chromiumcodereview.appspot.com/13932020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@195192 0039d316-1c4b-4281-b951-d872f2087c98